1. Field of the Invention
This invention generally relates to a bicycle crank. More specifically, the present invention relates to a bicycle crank having a bicycle crank arm that is non-rotatably mounted on a crank axle of a bicycle.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle crank.
A bicycle crank is a component for connecting a pedal to a crank axle, and is also a motion-transmitting member for transmitting pedal force from the pedal. The technological requirements of the crank include high strength in order to prevent damage or deformation despite the crank being repeatedly subjected to loads from the pedal, and high rigidity in order to prevent deformation or unpleasant sensations when the pedal is depressed. The crank must also be as lightweight as possible in order to reduce the weight of the entire bicycle.
To fulfill these requirements, cranks have been primarily made of aluminum alloys in the past. Specific known examples include high-strength aluminum alloys such as Alloy 7075, and alloys having hollowed structures in order to further reduce weight. However, there is a limit to reducing weight by means of an aluminum alloy alone. In view of this, metal crank axles have been fixed to cranks reinforced with a fiber-reinforced resin shell in the past (see U.S. Patent application Publication No. 2005/0011304). In these conventional cranks, the periphery of the aluminum crank is reinforced with a fiber-reinforced resin. A connecting hole for connecting the hollow crank axle is formed in the proximal end of the crank, and a crank axle is fixed in the connecting hole by press-fitting, for example. Therefore, the connecting hole is exposed in the portion of the crank connected to the crank axle.
Another conventional example is a crank having a hollowed structure in which a fiber-reinforced resin is used on the shell of the crank (see, for example, Japanese Laid-Open Patent Application No. 2003-72666). In a conventional bicycle crank, a fiber-reinforced resin shell covers the peripheries of the insert and the core. Specifically, fiber-reinforced resin tape is wound to form the peripheries of the insert and the core, and a crank is formed. The insert is used without any modification, but the core must be extracted from the crank after being formed, which complicates the crank manufacturing process and makes it difficult to form a precise shape.
In a configuration in which the crank is reinforced by a conventional fiber-reinforced resin, a connecting hole for press-fitting the crank axle into the proximal end of the crank is exposed to the exterior. The design of the crank is compromised when the connecting hole can be seen in the crank.
Moreover, if two shell members are joined to the insert members, a stress acting to twist the crank will act on the shell members when the pedal is depressed such that a force is transmitted through the shell members from the pedal connecting portion of the crank to the insert member of the crank axle connecting portion of the crank. Consequently, there is the possibility that a force acting to cause relative displacement between the shell members and the insert members could occur. If such a displacement force occurs, there is the possibility that the shell members and the insert member will peel apart from each other.
In cases in which the two shell members are bonded, internal pressure increases as the precision of the shapes increases. Thus, the adhesive applied to the two members may be forced to leak out when internal pressure increases. When the adhesive leaks out, bonding strength is insufficient, and the leaked adhesive adheres to the exterior, compromising the appearance.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle crank. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.